Moisture detecting apparatus for recording material and image forming apparatus

ABSTRACT

A moisture detecting apparatus includes: a light emitting unit including a first light source configured to emit light having a first wavelength as a peak wavelength, and a second light source configured to emit light having a second wavelength as a peak wavelength; a detecting unit configured to detect a first detection value indicating an extent to which the light emitted from the first light source is transmitted through a recording material, and a second detection value indicating an extent to which the light emitted by the second light source is transmitted through the recording material, based on a light receiving result of a light receiving unit; and a determination unit configured to determine a value related to a moisture content of the recording material based on the first detection value and the second detection value.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a moisture detecting apparatus thatdetects a value related to moisture content contained in a recordingmaterial and an image forming apparatus including the moisture detectingapparatus.

Description of the Related Art

Japanese Patent Laid-Open No. 2013-57513 and Japanese Patent Laid-OpenNo. H08-82598 disclose configurations for detecting moisture contentcontained in an object to be measured. In Japanese Patent Laid-Open No.2013-57513, moisture content is detected by detecting inner scatteredlight of a recording material using light at an absorption wavelength ofwater (1450 nm) and light at a non-absorption wavelength of water (1300nm). Also, in Japanese Patent Laid-Open No. H08-82598, moisture contentis detected by emitting light at an absorption wavelength of water andlight at a non-absorption wavelength of water onto an object to bemeasured, and detecting transmitted light or reflection light from theobject to be measured. In addition, Japanese Patent Laid-Open No.H09-210902 and Japanese Patent Laid-Open No. H09-61351 also discloseconfigurations in which light in an absorption wavelength range of waterand light in a non-absorption wavelength range of water are emitted ontoa detection target whose moisture content is to be detected and themoisture content of the detection target is detected.

However, in the configurations described in the above documents, it isnecessary to provide a light source that emits light at 1450 nm and 1940nm which are absorption wavelength of waters, and a light receivingelement with which a necessary light-receiving sensitivity in thesewavelengths can be obtained. Specifically, an expensive optical elementsuch as an LED or a photo-diode using InGaAs (Indium Gallium Arsenide)as a material is necessary, and therefore the cost is increased.

SUMMARY OF THE INVENTION

According to an aspect of the present invention, a moisture detectingapparatus includes: a light emitting unit including a first light sourceconfigured to emit light having a first wavelength of visible light ornear-infrared light as a peak wavelength, and a second light sourceconfigured to emit light having a second wavelength of visible light ornear-infrared light that is longer than the first wavelength as a peakwavelength; a light receiving unit configured to receive light emittedfrom the first light source and transmitted through a recordingmaterial, and light emitted by the second light source and transmittedthrough the recording material; a detecting unit configured to detect afirst detection value indicating an extent to which the light emittedfrom the first light source is transmitted through the recordingmaterial, and a second detection value indicating an extent to which thelight emitted by the second light source is transmitted through therecording material, based on a light receiving result of the lightreceiving unit; and a determination unit configured to determine a valuerelated to a moisture content of the recording material based on thefirst detection value and the second detection value.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a configuration diagram of an image forming apparatusaccording to an embodiment.

FIG. 2A is a configuration diagram of a moisture detecting apparatusaccording to an embodiment.

FIG. 2B is a configuration diagram of a moisture detecting apparatusaccording to an embodiment.

FIG. 3A is a diagram for illustrating a moisture detection principleaccording to an embodiment.

FIG. 3B is a diagram for illustrating a moisture detection principleaccording to an embodiment.

FIG. 4 is a diagram for illustrating moisture determination informationaccording to an embodiment.

FIGS. 5A and 5B are flowcharts of moisture detection processing for arecording material according to an embodiment.

FIG. 6 is a diagram for illustrating moisture determination informationaccording to an embodiment.

FIG. 7 is a diagram for illustrating basis weight determinationinformation according to an embodiment.

FIG. 8 is a perspective view of a moisture detecting apparatus accordingto an embodiment.

FIG. 9 is a configuration diagram of a moisture detecting apparatusaccording to an embodiment.

FIG. 10 is a configuration diagram of a moisture detecting apparatusaccording to an embodiment.

FIG. 11 is a diagram for illustrating a positional relationship ofconstituent elements of a moisture detecting apparatus according to anembodiment.

FIG. 12 is a diagram for illustrating an operation of a moisturedetecting apparatus according to an embodiment.

FIG. 13 is a diagram for illustrating an operation of a moisturedetecting apparatus according to an embodiment.

FIG. 14 is a diagram for illustrating an operation of a moisturedetecting apparatus according to an embodiment.

FIG. 15 is a diagram for illustrating an operation of a moisturedetecting apparatus according to an embodiment.

FIG. 16 is a configuration diagram of a moisture detecting apparatusaccording to an embodiment.

FIG. 17 is a configuration diagram of a moisture detecting apparatusaccording to an embodiment.

FIG. 18 is a diagram for illustrating an operation of a moisturedetecting apparatus according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

In the following, exemplary embodiments of the present invention will bedescribed with reference to the drawings. Note that, the followingembodiments are exemplary and the present invention is not limited tothe contents of the embodiments. In addition, in the following drawings,constituent elements that are not necessary for the description of theembodiments are omitted.

First Embodiment

FIG. 1 is a schematic configuration diagram of an image formingapparatus 1 including a moisture detecting apparatus according to thisembodiment. The image forming apparatus 1 forms color images bysuperimposing toner images formed with toners (developing materials) ofthe four colors yellow (Y), magenta (M), cyan (C), and black (B),respectively. In FIG. 1, Y, M, C, and K suffixed to the reference signsindicate that the colors of the toner related to forming by thecorresponding members are yellow, magenta, cyan, and black,respectively. Note that, if the toner colors do not need to bedistinguished in the following description, reference signs withoutalphabetical suffixes are used.

A photosensitive member 11 is an image carrier, and, when forming animage, is rotationally driven in a direction shown by the arrow in thediagram. A charge roller 12 charges a surface of the photosensitivemember 11 to a uniform potential. A scanner 13 scans and exposes thecharged photosensitive member 11 with light and forms an electrostaticlatent image on the photosensitive member 11. A developing unit 14includes a toner of the corresponding color, causes the toner to adherethe electrostatic latent image on the photosensitive member 11 by adeveloping bias output by a developing roller 15, and thereby forms atoner image on the photosensitive member 11. A primary transfer roller16 outputs a primary transfer bias and transfers the toner image on thephotosensitive member 11 to an intermediate transfer belt 17. Theintermediate transfer belt 17 is rotationally driven dependent on therotation of a driving roller 18 when forming an image. The toner imagesformed on the photosensitive members 11 are transferred to therotationally driven intermediate transfer belt 17 in a superimposedmanner, whereby a multi-color toner image can be formed. Also, the tonerimages transferred to the intermediate transfer belt 17 are conveyed toa position opposing the secondary transfer roller 19 by rotation of theintermediate transfer belt 17.

Also, a recording material P in a paper feeding cassette 2 is fed to aconveyance path by a paper feeding roller 4, and conveyed to a positionopposing the secondary transfer roller 19 by a pair of conveyancerollers 5 and a pair of registration rollers 6. The secondary transferroller 19 outputs a secondary transfer bias and transfers the tonerimage on the intermediate transfer belt 17 to the recording material P.The recording material P to which the toner image was transferred isconveyed to a fixing unit 20. The fixing unit 20 applies heat andpressure to the recording material P and fixes the toner image on therecording material P. The recording material P on which the toner imagewas fixed is discharged to the outside of the image forming apparatus 1by a paper discharge roller 21. In FIG. 1, members surrounded by adotted line indicated by a reference sign 40 constitute an image formingunit that forms an image on the recording material P.

A registration sensor 3 that detects the recording material P isprovided on the downstream side in the conveyance direction of therecording material relative to the pair of registration rollers 6. Also,a recording material discriminating apparatus 30 is provided on thedownstream side of the registration sensor 3 and on the upstream siderelative to the secondary transfer roller 19 in the conveyancedirection. The recording material discriminating apparatus 30 includes abasis weight detecting unit 31 that has a transmitting unit 33 and areceiving unit 34 and detects a basis weight of the recording materialP, and a surface property detecting unit 32 that detects a surfaceproperty of the recording material P. Moreover, a moisture detectingapparatus 35 is provided on the downstream side of the recordingmaterial discriminating apparatus 30 and on the upstream side of thesecondary transfer roller 19 in the conveyance direction. The moisturedetecting apparatus 35 is provided with a moisture detecting sensor unit36 including a light emitting unit 37 and a light receiving unit 38, anda moisture detecting control unit 39.

A control unit 10 of the image forming apparatus 1 performs control ofthe whole of the image forming apparatus 1, and is provided with atleast one processor and a nonvolatile memory that stores program anddata used by the processor, a RAM used as a work area of the processor,and the like. The control unit 10, for example, decides a print modecorresponding the kind of the recording material P that was detected bythe recording material discriminating apparatus 30, and collectivelycontrols the operations of the image forming apparatus 1.

Next, the moisture detecting apparatus 35 will be described. FIG. 2A isa block diagram of the moisture detecting apparatus 35. A moisturedetecting sensor unit 36 includes the light emitting unit 37 and thelight receiving unit 38 that are provided on opposite sides of theconveyance path of the recording material P, and light emitted from thelight emitting unit 37 is received by the light receiving unit 38. Here,the detailed configurations of the light emitting unit 37 and the lightreceiving unit 38, which form a principle portion of the moisturedetecting sensor unit 36, are shown in FIG. 2B.

The light emitting unit 37 is constituted by a light emitting element 37a, a light emitting element 37 b, and a drive circuit for driving theseelements (not shown). In this embodiment, the light emitting element 37a is an LED that emits light having a peak wavelength of 560 nm, and thelight emitting element 37 b is an LED that emits light having a peakwavelength of 850 nm. The wavelength band from approximately 400 to 800nm is generally called the visible light range, and the wavelength bandfrom approximately 800 to 2500 nm is generally called the near-infraredlight range. Accordingly, in the following, light emitted from the lightemitting element 37 a is denoted as “visible light”, and light emittedfrom the light emitting element 37 b is denoted as “near-infrared light”to distinguish between the two kinds of light. Note that theabove-described wavelengths of the light emitting elements 37 a and 37 bare merely examples, and they may be any wavelengths as long as they arewithin the visible light range or the near-infrared light range.

The visible light emitted from the light emitting unit 37 a isirradiated onto the recording material P via an aperture 37 c.Similarly, the near-infrared light emitted from the light emittingelement 37 b is irradiated onto the recording material P via an aperture37 d. The apertures 37 c and 37 d are provided for regulating theirradiated area on the surface of the recording material P, and forcausing the light transmitted through the recording material P to bereceived in a desired range on the light receiving unit 38. However, ifthe light emitting elements 37 a and 37 b emit light with highdirectivity, it is not necessary to provide the apertures 37 c and 37 d.

The light receiving unit 38 is provided with a light receiving element38 a and a light receiving element 38 b. The light receiving elements 38a and 38 b are photo electronic conversion elements such asgeneral-purpose CMOS sensors. Note that it is possible to use sensorsusing semiconductor silicon such as Si photodiodes, Si phototransistors,CCD sensors, and NMOS sensors, as the light receiving elements. Also,sensors whose light-receiving surface is area shaped or line shaped alsocan be used. In general, these photo electronic conversion elements havelight receiving sensitivity in a wavelength band from approximately 400to 1000 nm. In other words, the light receiving elements 38 a and 38 bhave light receiving sensitivity in a wavelength band including the peakwavelengths of the light emitting element 37 a and the light emittingelement 37 b.

Visible light and near-infrared light transmitted through the recordingmaterial P are respectively received by the light receiving elements 38a and 38 b. Note that, in this embodiment, the two light receivingelements 38 a and 38 b respectively corresponding to the two lightemitting elements 37 a and 37 b are used. However, it is sufficient ifthe transmitted light emitted from the light emitting elements 38 a and38 b that is transmitted through the recording material P can bedistinguished from each other and detected, and the configuration of themoisture detecting sensor unit 36 is not limited to the configurationshown in FIG. 2B. For example, if the transmitted light emitted from thelight emitting elements 37 a and 37 b can be irradiated onto differentranges of the light receiving element, and the light receiving elementcan separately output signals indicating the received light amounts oftransmitted light emitted from the light emitting element 37 a andtransmitted light emitted from the light emitting element 37 b, it ispossible to use one light receiving element. Moreover, if control isperformed such that the light emitting timings of the light emittingelements 38 a and 38 b are differentiated, the light receiving amountcan be detected individually even if the light receiving ranges of thetransmitted light emitted from the light emitting elements 38 a and 38 boverlap. Furthermore, regarding the distance between the light emittingelements, the apertures and the light receiving elements and theemission angle of light, it is sufficient if the transmitted light ofthe recording material P can be received, and, for example, aconfiguration can be applied in which light is obliquely emitted towardthe recording material and the light receiving surface.

Returning to FIG. 2A, the moisture detecting control unit 39 will bedescribed. The moisture detecting control unit 39 performs ON/OFFcontrol of the lights emitted from the light emitting elements 37 a and37 b of the light emitting unit 37, and light amount control (lightintensity control), of the light emitting unit 37. Note that thesecontrols are performed based on the control signals from the controlunit 10. The light emission amount of the light emitting elements 37 aand 37 b is controlled such that the amount of light that is transmittedthrough the recording material P is the amount that is receivable by thelight receiving elements 38 a and 38 b. Note that the optimal lightemission amount differs depending on characteristics of the lightemitting elements and the light receiving elements. Also, in a lightemitting element such as an LED, the light emission amount may fluctuatetemporally due to the influence of voltage fluctuation of the drivingcircuit in some cases, which causes a decrease in the detection accuracyof moisture content. In this case, it is possible to stabilize the lightemission amount by a constant current circuit or the like, for example.Furthermore, the moisture detecting control unit 39 outputs controlsignals that control the light receiving timing to the light receivingunit 38. By doing this, the light receiving times of the light receivingelements 38 a and 38 b are controlled to be equal to each other.

In addition, the moisture detecting control unit 39 obtains lightreceiving data indicating the light receiving amounts of visible lightand near-infrared light from the light receiving unit 38, and calculatesa value related to the moisture amount (moisture content) of therecording material P based on the light receiving data. Then, moisturecontent data indicating a value related to the calculated moisturecontent is input to the control unit 10. Note that the moisturedetecting control unit 39 can be realized on an application specificintegrated circuit (ASIC), and in this embodiment, the moisturedetecting control unit 39 is realized on an ASIC. However, it is alsopossible to realize the moisture detecting control unit 39 by causingthe processor of the control unit 10 of the image forming apparatus 1 toexecute a program.

The control unit 10 of the image forming apparatus 1 performs output ofthe control signal to the moisture detecting control unit 39, andcontrols image forming conditions according to the moisture content dataobtained from the moisture detecting apparatus 35. For example, thecontrol unit 10 controls the secondary transfer bias that is a transfervoltage output by the secondary transfer roller 19 and a transfercurrent flowing due to the secondary transfer bias according to themoisture content of the recording material P. Also, the control unit 10controls a fixing temperature of the fixing unit 20 according to thepercentage of moisture content of the recording material P.Specifically, since a resistance of the recording material P increaseswhen the moisture content of the recording material P is low, thecontrol unit 10 increases the secondary transfer bias such that thetransfer current increases. Also, since there is a concern of a fixingfailure when the moisture content of the recording material P is high,the control unit 10 increases the fixing temperature.

In the following, calculation of the percentage of moisture contentwhich is a value related to moisture content of the recording materialwill be described. First, the light receiving amounts when the lightreceiving elements 38 a and 38 b are caused to receive the light emittedfrom the light emitting elements 37 a and 37 b without the light beingtransmitted through the recording material P are hereinafter calledlight receiving amounts without paper. Also, the light receiving amountswhen the light receiving elements 38 a and 38 b are caused to receivethe light emitted from the light emitting elements 37 a and 37 b afterthe light has been transmitted through the recording material P arehereinafter called light receiving amounts with paper. At this time,transmission characteristics of the light emitted from each of the lightemitting elements 37 a and 37 b, that is, a detection value indicatingthe extent to which the light is transmitted through the recordingmaterial P, can be calculated using the following formula (1), forexample.Detection value=light receiving amount with paper×coefficient/lightreceiving amount without paper  (1)

In other words, a detection value indicating the transmissioncharacteristics of the recording material P is obtained by multiplyingthe ratio of a light receiving amount with paper and a light receivingamount without paper by a coefficient. Here, the coefficient is forcorrecting the difference between the light emitting amounts of thelight emitting elements 37 a and 37 b, and the difference between thelight receiving sensitivities (spectral sensitivity characteristics) andthe light receiving wavelengths of the light receiving elements 38 a and38 b and obtaining a normalized light receiving amount with paper, andis calculated and stored in the moisture detecting control unit 39 inadvance. Therefore, the light receiving amount with paper normalizedusing the coefficient and the light receiving amount without paper canbe said to indicate the transmitted light amount that is transmittedthrough the recording material P when the light emitting elements 37 aand 37 b are caused to emit light at a predetermined light emissionintensity. For this reason, the detection value is hereinafter referredto as the transmitted light amount. Note that, for example, if the lightemission intensity of the light emitting elements 37 a and 37 b and thesensitivity of the light receiving elements 38 a and 38 b are adjustedin advance, the light receiving amount with paper is set as thetransmitted light amount.

Next, the relationship between the transmitted light amount of therecording material P and the moisture content of the recording materialP will be described. FIG. 3A shows the transmitted light amounts of therecording material P for visible light and near-infrared light, in a drystate without containing moisture. Since light is more easilytransmitted through the recording material P as the wavelength becomeslonger, the transmitted light amount of near-infrared light is largerthan that of visible light.

On the other hand, when the recording material P contains moisture, thetransmission characteristic of the recording material P changesdepending on the moisture content contained in the recording material P.One of the factors that lead to this change is a change in the diffusedreflection characteristics on the surface of the recording material P.Specifically, if light is irradiated onto the recording material P,diffused reflection occurs on the surface of the recording material Pdue to irregularity of plant fibers that are a main component of therecording material P. Here, if the moisture content contained in therecording material P changes, the boundary condition of the surface ofthe recording material P changes, and the diffused reflection amount onthe surface of the recording material P changes. Specifically, if themoisture content contained in the recording material P increases, thediffused reflection amount on the recording material P decreases, andthus the transmitted light amount of the recording material P increases.Note that wavelength dependency of diffused reflection characteristicsis small. Therefore, although the transmitted light amounts of visiblelight and near-infrared light change depending on the change in thediffused reflection characteristics due to a change in the moisturecontent contained in the recording material P, the amount of the changeis substantially the same.

In addition, one of the factors which lead to a change in thetransmission characteristics of the recording material P is absorptionof light by moisture contained in the recording material P. Water has acharacteristic of absorbing light (light absorption characteristic), andthe extent of absorption differs depending on the wavelength of thelight. Specifically, as the wavelength becomes longer, the absorptionamount increases. Here, a decrease of the transmitted light amount basedon the light absorption characteristics due to an increase in themoisture content of the recording material P is smaller than an increaseof the transmitted light amount based on the diffused reflectioncharacteristics. That is, if the moisture content of the recordingmaterial P increases, the transmitted light amount of near-infraredlight and visible light increase as a whole, but the increase of thetransmitted light of near-infrared light is smaller than the increase ofthe transmitted light amount of visible light. FIG. 3B shows thisrelationship. The transmitted light amount of the recording material Pin a state of containing moisture increases compared with the recordingmaterial P in a dry state shown in FIG. 3A. Note that the increase ofvisible light is larger than that of near-infrared light due to thewavelength dependency of the light absorption characteristics.

In this embodiment, the difference between the transmitted light amountof visible light and the transmitted light amount of near-infrared lightis set as an evaluation value for evaluating the moisture content of therecording material P. Note that the difference between the light amountsis calculated using the following the formula (2).Difference between the light amounts=transmitted light amount ofnear-infrared light−transmitted light amount of visible light  (2)

As described above, since there is almost no wavelength dependency inthe change in the transmitted light amount based on the diffusedreflection characteristics when moisture content of the recordingmaterial P changes, the change in the transmitted light amount based onthe diffused reflection characteristics is balanced out in calculationof the difference between the light amounts. On the other hand, thechange in the transmitted light amount based on the light absorptioncharacteristics when the moisture content of the recording material Pchanges has a dependency on wavelength, and therefore the differencebetween the light amounts changes when moisture content of the recordingmaterial P changes.

FIG. 4 shows the relationship between the percentage of moisture contentof the recording material P and the difference between the lightamounts. Note that the percentage of moisture content denotes the ratio(%) of the moisture content of the recording material P relative to thebasis weight of the recording material P, and is a value indicating themoisture content of the recording material P. Note that FIG. 4 shows ameasurement result of the percentage of moisture content and thedifference between the light amounts when using plain paper whose basisweight is 60 g (60 g/m² paper) as the recording material P. As describedwith reference to FIGS. 3A and 3B, the difference between the lightamounts decreases as the percentage of moisture content of the recordingmaterial P increases. Moisture determination information such as aformula, a table or the like, indicating the relationship shown in FIG.4 is stored in the moisture detecting control unit 39 in advance. Then,the moisture detecting control unit 39 determines the percentage ofmoisture content based on the moisture determination information and thelight amount difference which is the evaluation value. Note that,although the percentage of moisture content is used as the valueindicating the moisture content of the recording material P in thisembodiment, it is also possible to use the information indicating therelationship between the light amount and the moisture content as themoisture determination information and thus calculate the moisturecontent. Moreover, although the difference between the transmitted lightamounts of visible light and near-infrared light is set as theevaluation value in this embodiment, as long as the value is related towater content, the present invention is not limited to the configurationin which the difference between the light amounts is set as theevaluation value. For example, the ratio between the transmitted lightamount of visible light and the transmitted light amount ofnear-infrared light can be set as the evaluation value. That is, aconfiguration is also possible in which the light amount ratio indicatedby the following formula (4) is used as the evaluation value.Ratio of the light amounts=transmitted light amount of near-infraredlight/transmitted light amount of visible light  (4)

FIGS. 5A and 5B are flowcharts of the determination processing for thepercentage of moisture content according to this embodiment. Upon thestart of image forming, in step S101, the moisture detecting controlunit 39 causes the light emitting elements 37 a and 37 b to emit light.In step S102, the control unit 10 detects the conveyance position of therecording material P by the registration sensor 3. After detecting therecording material P in step S102, the control unit 10, in step S103,stands by for a predetermined time. This stand-by time is the time takenfor the recording material P to reach a predetermined position on theupstream side relative to a position on the light path from the lightemitting unit 37 to the light receiving unit 38. When the predeterminedtime elapses in step S103, the control unit 10 controls the moisturedetecting control unit 39 such that the measurement of the lightreceiving amount without paper is performed for visible light andnear-infrared light in steps S104 and S204. Note that the measurement ofthe light receiving amount without paper is performed at the positionjust before the recording material P arrives on the light path from thelight emitting unit 37 to the light receiving unit 38 is to suppress theinfluence of temporal fluctuation of light emitting intensity of thelight emitting unit 37 in the measurement of light receiving amountwithout paper and light receiving amount with paper. After themeasurement of light receiving amount without paper, the control unit10, in step S105 and step S205, stands by for a predetermined time takenby the recording material P to reach the position at which the lightreceiving amount with paper can be measured. Thereafter, in step S106and S206, the control unit 10 controls the moisture detecting controlunit 39, and thereby the moisture detecting control unit 39 measures thelight receiving amount with papers for visible light and near-infraredlight.

In steps S107 and S207, the moisture detecting control unit 39calculates the transmitted light amounts of visible light andnear-infrared light using formula (1), and in steps S108 and S208, thetransmitted light amounts of visible light and near-infrared light arestored. In steps S109 and S209, the control unit 10 determines whetheror not the recording material P has left the position at which the lightreceiving amount with paper can be measured, and if not, the controlunit 10 controls the moisture detecting control unit 39 (so as) torepeatedly perform the measurement of the light receiving amount withpaper and calculation and storage of the transmitted light amounts. Whenthe recording material P leaves the position at which the lightreceiving amount with paper can be measured, in steps S110 and S120, themoisture detecting control unit 39 calculates the average value of themultiple transmitted light amounts measured for visible light andnear-infrared light. In step S111, the moisture detecting control unit39 calculates the evaluation value using the average value of thetransmitted light amounts for visible light and near-infrared light.Then, the moisture detecting control unit 39 determines the percentageof moisture content of the recording material P based on the moisturedetermination information set in advance and the evaluation value.

As described above, in this embodiment, the value indicating the watercontent of the recording material is calculated using light sources thatemit visible light and near-infrared light and light receiving elementshaving sensitivity to visible light and near-infrared light. That is,the moisture content of the recording material can be detected withoutusing a light receiving element having light receiving sensitivity to1450 nm and 1940 nm, which are absorption wavelengths of water. Notethat light receiving elements having sensitivity to visible light andnear-infrared light are common and not expensive. Also, since there isvariability in the thickness and density of the recording material Pdepending on the position thereof, variability may occur in the lightreceiving amount with paper depending on the measurement position.However, by detecting the light receiving amount with paper multipletimes and calculating the evaluation value using the average value ofthe light receiving amount with paper, it is possible to suppressvariability in light receiving amount with paper depending on themeasurement position, and detect the value related to moisture contentwith high accuracy. Note that, a configuration is also possible in whichthe light receiving areas of the light receiving elements 38 a and 38 bare widened, such as by using area sensors, instead of performing thedetection of the light receiving amount with paper multiple times. Also,by performing the measurement of light receiving amount without paperand the measurement of light receiving amount with paper in apredetermined time, it is possible to suppress the influence of temporalfluctuation of light emitting intensity of the light emitting elements37 a and 37 b, and detect the value related to the moisture content withhigh accuracy. Furthermore, by performing measurement of the lightreceiving amounts without paper and the light receiving amounts withpaper for visible light and near-infrared light in parallel, it ispossible to detect the value related to moisture content with highaccuracy and in short time.

Note that the present invention is not limited to the configuration inwhich the light emitting element 37 a emits visible light and the lightemitting element 37 b emits near-infrared light. A configuration is alsopossible in which both light emitting elements 37 a and 37 b emitsvisible light or near-infrared light, as long as there are twowavelengths in which the amounts of change in the transmitted lightamount due to the change in water content of the recording material Pare different.

Second Embodiment

Next, regarding a second embodiment, the difference from the firstembodiment will be mainly described. In this embodiment, the basisweight of the recording material P detected by the recording materialdiscriminating apparatus 30 is also used for determination of the valuerelated to moisture content.

The basis weight detecting unit 31 of the recording materialdiscriminating apparatus 30 shown in FIG. 1 is an ultrasonic wave sensorthat detects the basis weight of the recording material P. The basisweight detecting unit 31 includes a transmitting unit 33 that transmitsultrasonic waves to the recording material P and a receiving unit 34that receives ultrasonic waves via the recording material P, and detectsthe basis weight of the recording material P according to an amplitudeof the received ultrasonic waves. Note that the basis weight detectingunit 31 is not limited to the use of an ultrasonic wave sensor, and maybe another type of sensor that detects the basis weight of the recordingmaterial, or a sensor that detects the thickness or the like of therecording material that is highly correlated with the basis weight.

FIG. 6 shows the relationship between the basis weight of the recordingmaterial P and the difference between the transmitted light amounts ofvisible light and near-infrared light, in other words, the light amountdifference, which is an evaluation value. FIG. 6 shows the relationshipbetween the percentages of moisture content of approximately 2%, 5%, and9%, and the basis weights of plain paper of 60 g/m² (60 g/m² paper), 68g/m² (68 g/m² paper), and 75 g/m² (75 g/m² paper). In the 60 g/m² paper,68 g/m² paper, and 75 g/m² paper in FIG. 6, the light amount differencechanges with change in the basis weight of the recording material P. Forthis reason, the basis weight of the recording material P is detected bythe basis weight detecting unit 31 and the percentage of water contentof the recording material P is determined based on the relationshipbetween the evaluation value (light amount difference) and thepercentage of moisture content according to the basis weight, and thusthe percentage of moisture content can be determined with high accuracy.

The determination processing of the percentage of moisture content isbasically similar to the first embodiment shown in FIGS. 5A and 5B.However, in this embodiment, when the recording material P passesthrough the recording material discriminating apparatus 30, the basisweight of the recording material P is determined by the recordingmaterial discriminating apparatus 30. Specifically, ultrasonic wavesobtained from the transmitting unit 33 via the recording material P arereceived by the receiving unit 34, and the amplitude value is measured.The recording material discriminating apparatus 30 determines the basisweight based on the information indicating the relationship between theamplitude value and the basis weights, which is set in advance. Then, inthis embodiment, the moisture determination information indicates therelationship between the evaluation value and the percentage of watercontent for the basis weights of the recording materials P, as shown inFIG. 6. Then, in step S112 in FIG. 5B, the moisture detecting controlunit 39 determines the percentage of moisture content based on themoisture determination information corresponding to the basis weightdetected by the recording material discriminating apparatus 30 and theevaluation value.

As described above, in this embodiment, by detecting the basis weight ofthe recording material, highly accurate moisture content detection ofthe recording material based on the basis weight becomes possible. Notethat, it is also possible to apply the configuration in which the basisweight is determined based on input through a touch panel and operationof a button by a user, instead of detecting the basis weight by therecording material discriminating apparatus 30.

Third Embodiment

Next, regarding this embodiment, the difference from the first andsecond embodiments will be mainly described. In the second embodiment,the basis weight of the recording material P is detected by the basisweight determination unit 31 of the recording material discriminatingapparatus 30. In this embodiment, the range of the basis weight of therecording material P is detected using near-infrared light emitted fromthe light emitting element 37 b of the moisture detecting sensor unit36. Accordingly, the basis weight detecting unit 31 can be omitted inthis embodiment.

FIG. 7 shows the relationship between the transmitted light amount andthe basis weight when near-infrared light is emitted onto the recordingmaterial P. The basis weight of the recording material P and thetransmitted light amount of near-infrared light are related to eachother, and as the basis weight increases, the transmitted lightdecreases. Note that, although the transmitted light amount increasesand decreases according to the percentage of moisture content of therecording material P, the increasing/decreasing range is comparativelysmaller than the range of increasing/decreasing caused by the differencebetween the basis weights. For this reason, the approximate value(range) of the basis weight of the recording material P can beidentified according to the transmitted light amount of near-infraredlight.

The determination processing of the percentage of moisture content isbasically similar to the first embodiment shown in FIGS. 5A and 5B. Notethat, in this embodiment, basis weight determination informationindicating the relationship between the transmitted light amount ofnear-infrared light and the basis weight is set in advance in themoisture detecting control unit 39. Then, the moisture detecting controlunit 39 determines the basis weight according to the basis weightdetermination information and the average value of the transmitted lightamounts of near-infrared light calculated in step S210 in FIG. 5B. Also,water content determination information indicating the relationshipbetween the evaluation value and the percentage of water content,regarding the basis weight of the recording material P, is set in themoisture detecting control unit 39 in advance. Then, the moisturedetecting control unit 39 determines the percentage of moisture contentbased on moisture determination information at the basis weight that wasdetermined based on the transmitted light amount of near-infrared lightin step S112.

As described above, also in this embodiment, similarly to the secondembodiment, by considering the basis weight of the recording material P,it is possible to detect the value related to the moisture content ofthe recording material with high accuracy. Also, in this embodiment, thebasis weight detecting unit 31 can be omitted. Note that, in thisembodiment, although the basis weight of the recording material P isdetermined based on the transmitted light amount of near-infrared light,it is also possible to determine the basis weight of the recordingmaterial P based on the transmitted light amount of visible light.

Fourth Embodiment

Next, regarding a fourth embodiment, the difference from the aboveembodiments will be mainly described. FIG. 8 is a perspective viewshowing the configuration of the moisture detecting apparatus 35according to this embodiment. The recording material P is conveyed inthe direction shown by the arrow T inside the moisture detectingapparatus 35, and in that process, a value related to moisture contentis detected. As shown in FIG. 8, by the biasing mechanism which is notshown, a pressing rotational body 133 presses the recording material Pconveyed on the conveyance path with a pressing force F to theconveyance path side. Note that the pressing rotational body 133 is adriven roller that is rotated in an R direction by the recordingmaterial P. That is, the recording material P is conveyed by the pair ofregistration rollers 6 and the secondary transfer roller 19 in a stateof being held by the pressing rotational body 133, and the pressingrotational body 133 is configured so as to be rotated by the conveyanceof the recording material P. By doing this, flapping of the recordingmaterial P is suppressed and the recording material P conveyed in astable state in the moisture detecting apparatus 35.

FIG. 9 is a diagram of the moisture detecting apparatus 35 viewed fromthe upstream side in the conveyance direction of the recording materialP. A light emitting unit 37 includes light emitting elements L1 and L2that respectively emit light at different wavelengths, such as at 560 nmand 850 nm, for example, on an electric board EB1. A light receivingunit 38 includes a line light receiving element LS provided on anelectric board EB2. The line light receiving element LS includes aplurality of light receiving elements arranged in a line (linearly) in adirection perpendicular to the conveyance direction of the recordingmaterial P. The line light receiving element LS is arranged so as to becapable of receiving light emitted from light emitting elements L1 andL2 that is transmitted through the recording material P, and the lightreceiving elements of the line light receiving element LS outputelectric signals according to the light receiving amount. As the lightreceiving elements included in the line light receiving element LS,inexpensive elements having light receiving sensitivity around the rangeof visible light and near-infrared light (approximately, 400 to 1000 nm)including light emitting light wavelengths of the light emittingelements L1 and L2 can be used. Accordingly, it is not necessary to useexpensive light receiving elements made of InGaAs having light receivingsensitivity in an absorption wavelength of water (e.g. 1450 nm, 1940 nm,etc.). Note that the light emitting elements L1 and L2 respectivelycorrespond to the light emitting elements 37 a and 37 b in the aboveembodiments. Also, the light receiving element that receives thetransmitted light from the light emitting element L1 among the pluralityof light receiving elements of the line light receiving element LScorresponds to the light receiving element 38 a in the aboveembodiments. Similarly, the light receiving element that receives thetransmitted light from the light emitting element L2 among the pluralityof light receiving elements of the line light receiving element LScorresponds to the light receiving element 38 b in the aboveembodiments. In this embodiment, the method for detecting the valuerelated to moisture amount (moisture content) included in the recordingmaterial P based on the output from the line light receiving element LSis similar to the above embodiments, and thus the description isomitted.

The pressing rotational body 133 is provided with two cylindricalmembers 331 and 332 having the same diameter that press the recordingmaterial P, and a connecting member 333 that connects the cylindricalmembers 331 and 332. The pressing rotational body 133 is constitutedwith a member that sufficiently transmits the wavelengths of the lightsemitted from the light emitting elements L1 and L2, such as atransparent member. Also, the diameter of the connecting member 333 isshorter than the diameter of the cylindrical members 331 and 332. Thisis to prevent the connecting member 333 from coming into contactdirectly with a glass surface that forms part of the conveyance path ofthe recording material P so as to not damage the glass surface with theconnecting member 333. Here, the glass surface is provided at a positionopposing the connecting member 333 such that the light emitted from thelight emitting elements L1 and L2 reaches the line light receivingelement LS. By preventing the glass from being damaged, decrease in thelater-described detection accuracy of the moisture content can besuppressed.

FIG. 10 is a cross-sectional view along a line A-A in FIG. 9, and FIG.11 is a diagram for describing a positional relationship of the members.The light emitting elements L1 and L2, a rotational center axis of thepressing rotational body 133, and the line light receiving element LSare provided so as to be located in substantially the same plane (in aplane PI in FIG. 11, corresponding to a dot-and-dash line in thevertical direction in FIG. 10) as shown in FIG. 11. Also, as shown inFIG. 11, the members are provided such that three lines consisting of avirtual line La connecting the light emitting elements L1 and L2, arotational center axis Lb of the pressing rotational body 133 and a lineLc in the direction in which the elements of the line light receivingelement LS are arranged in parallel to each other and in the flat planePI. Moreover, a distance L_(a-b), between the virtual line La and therotational center axis Lb and a distance L_(b-c) between the rotationalcenter axis Lb and the line Lc are set to be substantially equal.

FIGS. 12 and 13 show a state in which the light emitting elements L1 andL2 are emitting light. Note that FIGS. 12 and 13 are diagrams viewedfrom the same position as FIG. 9 and FIG. 10, respectively. In FIGS. 12and 13, light emitted from the light emitting element L1 is indicated byL1L, and light emitted from the light emitting element L2 is indicatedby L2L. As shown in FIG. 12, the light L1L and the light L2L emittedfrom the light emitting elements L1 and L2 reach the line lightreceiving element LS while spreading in a direction orthogonal to theconveyance direction of the recording material P. Then, based onelectrical signals output by the light receiving elements of the linelight receiving element LS, the light receiving amount of the light L1Land the light receiving amount of the light L2L can be determinedrespectively.

When passing through the transparent pressing rotational body 133, thelight L1L and the light L2L are attenuated due to inner reflection,loss, and the like. Moreover, the light L1L and the light L2L aregreatly attenuated due to passing through the recording material P, andreach the line light receiving element LS. Note that, as shown in FIG.13, the pressing rotational body 133 having a circular cross section hasa lens-like effect, and in the conveyance direction of the recordingmaterial P, spreading of the light emitted from the light emittingelements L1 and L2 is suppressed, and the light can be collected to theline light receiving element LS. In addition, due to the transparentpressing rotational body 133, the line light receiving element LS candetect the light receiving amount while holding the recording materialP. Accordingly, it is possible to suppress the influence of moisturecontent being locally distributed in the conveyance direction of therecording material P, and detect the average moisture content in thesurface of the recording material P.

As described above, in this embodiment, by the transparent pressingrotational body 133 pressing the recording material, flapping of therecording material is suppressed. Light is emitted onto the recordingmaterial via this transparent pressing rotational body 133, and thevalue related to the moisture content of the recording material isdetected according to the transmitted light amount. Accordingly, it ispossible to suppress the fluctuation of the transmitted light amount dueto flapping of the recording material, and detect the value related tothe moisture content of the recording material with high accuracy. Notethat a configuration is also possible in which only an area of thepressing rotational body 133 through which the light L1L and the lightL2L passes is constituted with a transparent member, instead ofconstituting the whole of the pressing rotational body 133 with atransparent member.

Fifth Embodiment

Next, regarding a fifth embodiment, the difference from the fourthembodiment will be mainly described. FIGS. 14 and 15 are configurationdiagrams of the moisture detecting apparatus 35 according to thisembodiment, and correspond to FIGS. 12 and 13 in the fourth embodiment.Note that constituent elements similar to the moisture detectingapparatus 35 according to the fourth embodiment are given the samereference signs and description thereof is omitted. In this embodiment,a pressing rotational body 134 is used instead of the pressingrotational body 133 in the fourth embodiment. Similarly to the fourthembodiment, the pressing rotational body 134 is provided with twocylindrical members 331 and 332 having the same diameter that press therecording material P, and a connecting member 343 that connects thecylindrical members 331 and 332. The two cylindrical members 331 and 332are arranged at different positions in the direction orthogonal to theconveyance direction of the recording material, and the connectingmember 343 is a member extending in the direction orthogonal to theconveyance direction of the recording material, and includes therotational axis of the pressing rotational body 34. However, thediameter of the connecting member 343 is set to be smaller than that ofthe connecting member 333 in the fourth embodiment. In other words, thearea of the cross section orthogonal to the rotational axis of theconnecting member 343 is set to be smaller than the area of the crosssection orthogonal to the rotational axis of the cylindrical members 331and 332. In addition, in the fourth embodiment, the rotational center ofthe pressing rotational body 133 is located on a line connecting thelight emitting elements L1 and L2 with the line light receiving elementLS in the conveyance direction of the recording material. In thisembodiment, as shown in FIG. 15, a position 138 of the rotational centerof the pressing rotational body 134 in the conveyance direction of therecording material is shifted by a predetermined distance to theupstream side in the conveyance direction of the recording material fromthe position 137 in the fourth embodiment. As such, as shown in FIG. 15,when viewed in the direction of the rotational axis of the rotationmember, each center line of the light paths does not pass through therotational axis of the rotation member, and the light paths intersectwith the direction of the rotational axis and a conveyance direction inwhich the sheet is conveyed.

Accordingly, the light L1L and the light L2L received by the line lightreceiving element LS do not pass through the connecting member 343. Notethat, as shown in FIG. 14, the light L1L and the light L2L received bythe line light receiving element LS include the light that have passedthrough the cylindrical members 331 and 332. However, it is alsopossible to adjust the area in which the line light receiving element LSis arranged such that the line light receiving element LS is configuredto receive only the light L1L and the light L2L that do not pass throughthe pressing rotational body 134. By doing this, the line lightreceiving element LS can receive a light in which the attenuation oflight caused by the pressing rotational body 134 is suppressed. Sincethe light receiving amount of the line light receiving element LSincreases, it is possible to detect the moisture content contained inthe recording material P with high accuracy.

Note that the shift amount of the rotational center to the upstream sidein the conveyance direction of the recording material is decided withinthe range in which flapping of the recording material P on the lightpath from the light emitting elements L1 and L2 to the line lightreceiving element LS can be suppressed. For an example, the shift amountis less than or equal to 5 mm. Alternatively, as shown in FIG. 15, aconfiguration is also possible in which the rotational center of thepressing rotational body is shifted in a range in which a lineconnecting the light emitting elements L1 and L2 with the lightreceiving element LS passes through the cylindrical members 331 and 332.Also, the direction of shifting the rotational center may also be thedownstream side in the conveyance direction of the recording material.

As described above, the connecting member 343 including the rotationalaxis of the pressing rotational body 134 is arranged at a position inwhich the connecting member 343 does not interfere with the light pathfrom the light emitting elements L1 and L2 to the line light receivingelement LS. By this configuration, the attenuation of light by thepressing rotational body 134 is suppressed, and thus it becomes possibleto detect the value related to the moisture content of the recordingmaterial with high accuracy. Note that, in this embodiment, the pressingrotational body 134 need not be formed with a transparent member.

Sixth Embodiment

Next, regarding a sixth embodiment, the difference from the fourthembodiment will be mainly described. FIGS. 16 and 17 are perspectiveviews showing a configuration of the moisture detecting apparatus 35according to this embodiment. Note that FIG. 17 is a diagram viewed fromupstream side in the conveyance direction of the recording material P,and FIG. 17 is a cross-sectional view along a line A-A in FIG. 16. Notethat constituent elements similar to those described in the fourthembodiment are given the same reference signs and description thereof isomitted. As shown in FIG. 16, in this embodiment, the arrangementpositions of the light emitting elements L1 and L2 are shifted in thedirection orthogonal to the conveyance direction compared to theconfiguration in the fourth embodiment. Although the arrangementposition is shifted to the right side in FIG. 16, shifting to the leftside is also possible. In addition, instead of the pressing rotationalbody 133, a pressing rotational body 136 constituted with a transparentmember 136A and a black member 136B (shaded area) is used. The blackmember 136B is provided so as to be located on a different side from theside to which the light emitting elements L1 and L2 are shifted. Inaddition, a light emitting element L3 and a light guide LG that guidesthe light emitted from the light emitting element L3 to the recordingmaterial P are provided on the same board as the line light receivingelement LS.

The light emitting element L3 and the light guide LG are provided todetermine the surface property of the recording material. The principleof determination of the surface property is disclosed in Japanese PatentLaid-Open No. 2014-114131, for example. In brief, light emitted from thelight emitting element L3 is irradiated onto the surface of therecording material P via the light guide LG, and the reflected light isreceived by the line light receiving element LS. There is a relationshipbetween the extent of irregularity of the surface of the recordingmaterial P and the reflected light amount. Accordingly, a tableindicating the relationship between the extent of irregularity and thereflected light amount is set in the image forming apparatus in advance,and the control unit 10 determines the surface property of the recordingmaterial based on the table and the light receiving amount of the linelight receiving element LS for the reflected light of the light emittedfrom the light emitting element L3.

FIG. 18 shows a state in which the light emitting elements L1, L2, andL3 are caused to emit light, and corresponds to FIG. 12 in the fourthembodiment. The light emitted from the light emitting elements L1 and L2is, similarly to the first embodiment, received by the line lightreceiving element LS via the transparent member 136A of the pressingrotational body 136. However, in this embodiment, since the lightemitting elements L1 and 12 are shifted to the right side in thediagram, the light L1L and the light L2L are received by the lightreceiving element of the line light receiving element LS in the righthalf of the diagram. On the other hand, the light emitted from the lightemitting element L3 is irradiated onto the surface of the recordingmaterial P from the lower side in the diagram, via the light guide LG.The light receiving element having an area that is different from thearea in which the light L1L and the light L2L of the line lightreceiving element LS is received the reflected light of the lightemitted from this light emitting element L3. The black member 136B ofthe pressing rotational body 136 is located on the upside of the lightreceiving area of the line light receiving element LS which receives thelight emitted from the light emitting element L3. That is, the blackmember 136B of the pressing rotational body 136 is arranged in aposition opposing the light receiving area of the line light receivingelement LS which receives the light emitted from the light emittingelement L3, via the recording material P. The black member 136Btransmits a smaller amount of light than the transparent member 136A.Accordingly, due to this black member 136B, it is possible to suppresstransmitted light from the recording material P that is emitted by thelight emitting elements L1 and L2 and external light from entering thelight receiving element of the line light receiving element LS thatreceives the reflected light of the light emitted from the lightemitting element L3. Therefore, it is possible to suppress deteriorationof the determination accuracy of the surface property of the recordingmaterial P.

As described above, in this embodiment, it is possible to provide themoisture detecting apparatus 35 with a function of determining thesurface property of the recording material, and thus the surfaceproperty detection unit 32 can be omitted and the image forming layercan be minimized.

OTHER EMBODIMENTS

Embodiments of the present invention can also be realized by a computerof a system or apparatus that reads out and executes computer executableinstructions (e.g., one or more programs) recorded on a storage medium(which may also be referred to more fully as a ‘non-transitorycomputer-readable storage medium’) to perform the functions of one ormore of the above-described embodiments and/or that includes one or morecircuits (e.g., application specific integrated circuit (ASIC)) forperforming the functions of one or more of the above-describedembodiments, and by a method performed by the computer of the system orapparatus by, for example, reading out and executing the computerexecutable instructions from the storage medium to perform the functionsof one or more of the above-described embodiments and/or controlling theone or more circuits to perform the functions of one or more of theabove-described embodiments. The computer may comprise one or moreprocessors (e.g., central processing unit (CPU), micro processing unit(MPU)) and may include a network of separate computers or separateprocessors to read out and execute the computer executable instructions.The computer executable instructions may be provided to the computer,for example, from a network or the storage medium. The storage mediummay include, for example, one or more of a hard disk, a random-accessmemory (RAM), a read only memory (ROM), a storage of distributedcomputing systems, an optical disk (such as a compact disc (CD), digitalversatile disc (DVD), or Blu-ray Disc (BD)™, a flash memory device, amemory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2017-078477, filed on Apr. 11, 2017 and Japanese Patent Application No.2017-078478, filed on Apr. 11, 2017, which are hereby incorporated byreference herein in their entirety.

What is claimed is:
 1. A detection device comprising: a first lightsource configured to emit first light on a sheet, the first light havinga peak wavelength that is included in a band from 400 nm to 800 nm; asecond light source configured to emit second light on the sheet, thesecond light having a peak wavelength that is longer than the peakwavelength of the first light and included in a band from 800 nm to 2500nm; a light receiving unit configured to receive the first light and thesecond light transmitted through the sheet; and a rotation memberconfigured to rotate and press the sheet, on which at least one of thefirst light and the second light is emitted, against a conveyance guidefor guiding the sheet, wherein, as viewed in a direction of a rotationalaxis of the rotation member, light paths from the first light source andthe second light source to the light receiving unit overlap with therotation member.
 2. The detection device according to claim 1, wherein,as viewed in the direction of the rotational axis of the rotationmember, each center line of the light paths does not pass through therotational axis of the rotation member, and the light paths intersectwith the direction of the rotational axis and a conveyance direction inwhich the sheet is conveyed.
 3. The detection device according to claim1, wherein, as viewed in the direction of the rotational axis of therotation member, the light paths pass through a position on a downstreamside of the rotational axis of the rotation member in a conveyancedirection in which the sheet is conveyed.
 4. The detection deviceaccording to claim 1, wherein the rotation member includes a firstrotating portion and a second rotating portion, and wherein the firstrotating portion and the second rotating portion are arranged in adirection of the rotational axis of the rotation member, and a diameterof the first rotating portion is shorter than a diameter of the secondrotating portion.
 5. The detection device according to claim 1, whereinthe rotation member includes a first cylindrical member, a secondcylindrical member, and a connecting member that connects the firstcylindrical member and the second cylindrical member, and wherein, asviewed in the direction of the rotational axis of the rotation member,the light paths do not overlap with the connecting member, and the lightpaths do overlap with the first cylindrical member and the secondcylindrical member.
 6. The detection device according to claim 1,wherein light receiving sensitivity of the light receiving unit rangesfrom 400 nm to 1000 nm.
 7. The detection device according to claim 1,wherein the peak wavelength of the second light is included in a bandfrom 800 nm to 1000 nm.
 8. The detection device according to claim 7,wherein the peak wavelength of the second light is 850 nm.
 9. Thedetection device according to claim 1, wherein the light receiving unitis configured to receive an amount of the first light and an amount ofthe second light.
 10. The detection device according to claim 1, furthercomprising: a third light source configured to emit third light on thesheet and provided on an opposite side from the first light source andthe second light source with respect to a path on which the sheet isconveyed, and wherein the light receiving unit is configured to receivethe third light reflected on the sheet.
 11. The detection deviceaccording to claim 10, wherein the light receiving unit is configured toreceive an amount of the third light.